Modal Analysis on Control Impact of Fully Rated Converters-Based PMSG-WECS Connected to Turbine-Generator

Abstract

The power converter-based wind energy conversion systems (WECS) connected to weak AC networks may cause subsynchronous interactions that can potentially lead to instability. The interaction between the WECS converters and a nearby turbine-generator (TG) may lead to severe torsional vibrations. This article investigates the impact of a fully rated converters-based permanent magnet synchronous generator WECS (PMSG-WECS) on the subsynchronous torsional interactions (SSTI) of a nearby multimass TG connected to series compensated transmission line. A simple but effective systematic approach of modal analysis using open-loop systems is proposed. The proposed approach is used to evaluate the impact of PMSG-WECS on SSTI. Further, the impact of PMSG-WECS is analyzed through the damping torque, eigenvalue analysis and transient simulation under various control modes of PMSG-WECS converters. The results demonstrate that the inclusion of PMSG-WECS increases the subsynchronous resonance frequency of the network, thereby reduces the damping of the torsional modes in the high-frequency range of subsynchronous resonance frequency. The negative damping effect of PMSG-WECS significantly reduces the damping of subsynchronous network mode, thereby can destabilize the system. Also, the negative damping impact of PMSG-WECS significantly reduces the damping of high-frequency torsional modes. As a result, the torsional interactions aggravate at lower compensation levels.